A new variant of the Gameover computer Trojan is targeting job seekers and recruiters by attempting to steal log-in credentials for Monster.com and CareerBuilder.com accounts.

Gameover is one of several Trojan programs that are based on the infamous Zeus banking malware, whose source code was leaked on the Internet in 2011. Like Zeus, Gameover can steal log-in credentials and other sensitive information by injecting rogue Web forms into legitimate websites when accessed from infected computers.

The ability to inject content into browsing sessions in real time has traditionally been used by computer Trojans to steal online banking credentials and financial information. However, cybercriminals are increasingly using this technique to compromise other types of accounts as well.

For example, in February, researchers from security firm Adallom found a Zeus variant that stole Salesforce.com log-in credentials and scraped business data from the compromised accounts.

The latest development involves a new Gameover variant that contains a configuration file to target Monster.com accounts, one of the largest employment websites in the world, security researchers from antivirus firm F-Secure said Tuesday in a blog post: http://www.f-secure.com/weblog/archives/00002687.html

“A computer infected with Gameover ZeuS will inject a new ‘Sign In’ button [into the Monster.com sign-in page], but the page looks otherwise identical,” they said.

After the victims authenticate through the rogue Web form the malware injects a second page that asks them to select and answer three security questions out of 18. The answers to these questions expose additional personal information and potentially enable attackers to bypass the identity verification process.

Targeting Monster.com is a new development, but the Gameover malware had already been targeting CareerBuilder.com, another large employment website, for some time.

Recruiters with accounts on employment websites should be wary of irregularities on log-in pages, especially if those accounts are tied to bank accounts and spending budgets, the F-Secure researchers said. “It wouldn’t be a bad idea for sites such as Monster to introduce two factor authentication beyond mere security questions.”

Unlike most other Zeus spinoffs, Gameover is also using peer-to-peer technology for command-and-control instead of traditional hosted servers, which improves its resilience to takedown efforts by security researchers.